With the spread of Internet and wide area Ethernet services, data centers are widely utilized. There are data centers that have various computers, communication devices, and the like located therein for operation.
As one of the standards related to 10 gigabit Ethernet, there is IEEE 802.1 Qau Congestion Notification (CN) standard. In this standard, an L2 switch where congestion occurs sends a congestion notification message (CNM) to a server that is considered to cause the congestion, so as to inhibit a traffic volume to be transmitted by the server that has received the CNM. Other than this, various methods of resolving congestion are also proposed (for example, refer to Japanese Laid-open Patent Publications Nos. 2004-104427, 2007-282037, and 2003-092593).